Systems for mounting mailbox posts in the ground are known. One such system has a stake coupled to a carrier. The carrier has a sidewall with four distinct sections. Each section is adjacent to two other sections and normal to the two other sections. The four sections provide a square perimeter delimiting a hollow. The hollow receives the mailbox post. One of the four sections has a gap forming a split along a length of the section's height. Adjustable threaded fasteners join the portions of this section split by the gap. Tightening the fasteners reduces the width of the gap contracting the perimeter formed by the four sections. The contraction fixes the portion of the post inserted into the carrier inside the carrier and fixes the post relative to the stake.